Sod, slurry-on-demand, casting method and charge

ABSTRACT

A SOD (slurry-on-demand) casting method and charge is provided for casting a low-solid-fraction, namely 10 to 30% solid-fraction, alloy.

BACKGROUND AND SUMMARY

The invention relates to SOD (slurry-on-demand) casting systems.

The present invention arose during continuing development efforts relating to SOD technology as shown and described in the following U.S. patents and applications, owned by the assignee of the present application, and all incorporated herein by reference: U.S. Pat. Nos. 6,399,017; 6,402,367; 6,432,160; 6,443,216; 6,611,736; 6,637,927; 6,742,567; 6,796,362; 6,845,809; 6,932,938; 6,991,670; 7,024,342; and U.S. patent application Ser. Nos. 10/617,307; 10/692,312; 10/845,311; 10/847,404; 10/989,137; 11/043,521.

The present invention enables application of the above noted SOD technology to a wide array of die cast alloys and die casting applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating slurry apparatus for implementing the SOD casting method in accordance with the invention.

FIG. 2 shows the vessel of FIG. 1.

FIG. 3 is a top view of the vessel of FIG. 2.

DETAILED DESCRIPTION

Referring to FIG. 1 and the above noted incorporated SOD patents, vessel 10 contains a semi-solid casting alloy 12 and is carried on a fixture 14 on a transfer device such as robotic arm 16. The alloy is heated, e.g. in a furnace as in the above incorporated SOD patents, to a molten liquid state, and then poured or discharged into vessel 10, which is surrounded by an optional cooling sleeve or jacket 18, and may be separated therefrom by air gaps such as 20 for controlled cooling, which jacket 18 is disposed within electromagnetic stirring device 22, e.g. a stator, supported by base plate 24 which may or may not be cooled. After cooling and magnetic stirring, the alloy is transferred while in a partial solid/liquid phase to a casting machine, all as is known and disclosed in the above noted and incorporated SOD patents. The noted transfer may be facilitated by a pouring spout 26 formed in the upper collar or lip of vessel 10, FIGS. 2, 3.

In the present methodology, a SOD (slurry-on-demand) casting method casts a low-solid-fraction, namely 10 to 30% by weight solid-fraction alloy. This is in contrast to prior solid-fraction ratios of 40 to 60%. By way of analogy, the noted prior 40 to 60% solid-fraction ratio provides an ice cream-like or jello-like billet, whereas a 10 to 30% solid-fraction ratio provides a soupy milkshake-like or oatmeal-like charge or billet. It is has been found that the latter ratio, namely a low-solid-fraction, namely 10 to 30% solid-fraction, enables usage of a wider array of die cast alloys, including 380, 383, 360, and Mercalloy (commercially produced under such Trademark by Mercury Marine Division, Brunswick Corporation) alloys. The present method provides a SOD, slurry-on-demand, casting method for casting a low-solid-fraction, namely 10 to 30% solid-fraction, alloy, including the steps of heating the alloy to a molten liquid state, e.g. in vessel 10 as above, cooling and stirring the alloy to nucleate and create a partial solid phase of the noted low-solid-fraction, and transferring the alloy while in the partial solid phase of the noted low-solid-fraction to a casting machine, as in the above noted incorporated SOD patents.

In the preferred embodiment of the present method, the alloy includes a pair of constituents of different melting point including a first constituent of a first melting point, and a second constituent of a second lower melting point. During the noted cooling and stirring step, the preferred embodiment of the present method cools the alloy below the first melting point but above the second melting point, whereafter the noted transferring step is performed. The first and second melting points are preferably selected close enough to each other such that during the cooling and stirring step, the solidification of the first constituent is limited to the noted low-solid-fraction until the second constituent begins to solidify, and then the transferring step is performed when the temperature of the alloy is between the noted first and second melting points.

In one preferred embodiment, the alloy is provided by aluminum as the first constituent and silicon as the second constituent. In this embodiment, it is preferred that the silicon content in the molten state increase from 9% to 12%±1% (in one preferred embodiment the latter being 12.6%) during the noted cooling step between the first and second melting temperatures whereby the amount of aluminum transitioning in phase from liquid to solid state is limited to the noted low-solid-fraction, wherein the eutectic composition of the alloy is at the noted 12.6% silicon.

Further in the preferred embodiment, the noted first constituent is nucleated and solidified by magnetic stirring, as in the above noted incorporated SOD patents. Further in the preferred embodiment, the first constituent is nucleated and solidified without introducing a foreign object into the molten alloy. This is in contrast to prior art systems incorporating a rotating cooled rod, e.g. a graphite rod, introduced into a crucible of alloy to initiate the nucleation of solid phase particles.

Further in the preferred embodiment, after the noted heating step, the alloy is transferred while in the molten liquid state to vessel 10, and then the cooling and magnetic stirring step is performed while the alloy is in vessel 10, and then the alloy is transferred in the noted partial solid phase of the noted low-solid-fraction from the vessel to the casting machine.

In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different configurations, systems, and method steps described herein may be used alone or in combination with other configurations, systems and method steps. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims. 

1. A SOD (slurry-on-demand) casting method for casting a low-solid-fraction, namely 10 to 30% solid-fraction, alloy, comprising heating said alloy to a molten liquid state, cooling and stirring said alloy to nucleate and create a partial solid phase of said low-solid-fraction, and transferring said alloy while in said partial solid phase of said low-solid-fraction to a casting machine.
 2. The method according to claim 1 wherein said alloy comprises a pair of constituents of different melting points comprising a first constituent of a first melting point, and a second constituent of a second lower melting point, and comprising, during said cooling and stirring step, cooling said alloy below said first melting point but above said second melting point, and then performing said transferring step.
 3. The method according to claim 2 comprising selecting said first and second melting points close enough to each other such that during said cooling and stirring step, the solidification of said first constituent is limited to said low-solid-fraction until said second constituent begins to solidify, and performing said transferring step when the temperature of said alloy is between said first and second melting points.
 4. The method according to claim 3 wherein said alloy comprises aluminum as said first constituent and silicon as said second constituent, and wherein the silicon content in said molten state increases from 9% to 12%±1% during said cooling step between said first and second melting temperatures whereby the amount of aluminum is limited to said low-solid-fraction.
 5. The method according to claim 4 wherein the eutectic composition of said alloy is at 12.6% silicon.
 6. The method according to claim 2 comprising nucleating and solidifying said first constituent by magnetic stirring and without introducing a foreign object into the molten alloy.
 7. The method according to claim 6 comprising, after said heating step, transferring said alloy while in said molten liquid state to a vessel, and performing said cooling and magnetic stirring step while said alloy is in said vessel, and then transferring said alloy in said partial solid phase of said low-solid-fraction from said vessel to said casting machine.
 8. A SOD (slurry-on-demand) casting alloy charge having a low-solid-fraction, namely 10 to 30% by weight solid-fraction.
 9. The SOD casting alloy charge according to claim 8 wherein said 10 to 30% solid-fraction ratio provides a soupy milkshake-like charge, in contrast to an ice cream-like billet provided by a 40 to 60% solid-fraction ratio.
 10. The SOD casting alloy charge according to claim 8 wherein said alloy comprises a pair of constituents of different melting points comprising a first constituent of a first melting point, and a second constituent of a second lower melting point.
 11. The SOD casting alloy charge according to claim 10 wherein said alloy is cooled below said first melting point but above said second melting point, and wherein said first and second melting points are close enough to each other such that during said cooling, the solidification of said first constituent is limited to said low-solid-fraction until said second constituent begins to solidify.
 12. The SOD casting alloy charge according to claim 11 wherein said alloy comprises aluminum as said first constituent and silicon as said second constituent, and wherein the silicon content in a molten state increases from 9% to 12%±1% during said cooling between said first and second melting temperatures whereby the amount of aluminum is limited to said low-solid-fraction.
 13. The SOD casting alloy charge according to claim 12 wherein the eutectic composition of said alloy is at 12.6% silicon.
 14. The SOD casting alloy charge according to claim 10 wherein said first constituent is nucleated and solidified by magnetic stirring and without introduction of a foreign object into a molten said alloy.
 15. The SOD casting alloy charge according to claim 8 wherein said 10 to 30% solid-fraction alloy is a die cast alloy selected from the group consisting of 380, 383, 360, and Mercalloy alloys. 